Turbine blade tip shroud

ABSTRACT

A turbine blade that may include a tip shroud, the tip shroud having one or more cooling cavities defined therein, an airfoil, the airfoil having at least one coolant passage defined therein, and a plurality of exit apertures defined through an outer wall of at least one of the cooling cavities that, in use, may allow a pressurized coolant to exit at least one of the cooling cavities. The coolant passage may extend through the airfoil such that the coolant passage is in fluid communication with the cooling cavity. And, the plurality of exit apertures may include at least one round exit aperture and at least one non-round exit aperture.

BACKGROUND OF THE INVENTION

The present invention relates to a blade for a turbine, e.g. aircraftengine, gas turbine, steam turbine, etc. More specifically, the presentinvention relates to hollow cavity tip shrouds and the cooling of aturbine blade tip shroud through the use of circulating coolant throughthe hollow cavity. As a non-limiting example, the invention and itsbackground are described with reference to a gas turbine.

The turbine blades of industrial gas turbines and aircraft enginesoperate in an extreme temperature environment. The thermal stresses andmetal temperatures associated with this environment may decrease theuseful operating life of the turbine blades. Cooling the turbine blades,and the component parts thereof, during operation may extend theiruseful operating life.

Many turbine blades include an airfoil and an integral tip shroudattached to the tip of the airfoil. The tip shroud, which attaches tothe outer edge of the airfoil, provides a surface area that runssubstantially perpendicular to the airfoil surface. The surface area ofthe tip shroud helps to hold the turbine exhaust gases on the airfoil(i.e., does not allow the exhaust gases to slide over the end of theairfoil blade) so that a greater percentage of energy from the turbineexhaust gases may be converted into mechanical energy by the turbineblades. Tip shrouds thusly improve the performance of the gas turbineengine. Further, it is desirable to have the entire outer surface of theairfoil covered by a tip shroud. However, tip shrouds and the connectionthey make to the airfoils become highly stressed during operationbecause of the mechanical forces applied via the rotational speed of theturbine. When these mechanical stresses are coupled with the thermalstresses and metal temperatures associated with extreme high temperatureenvironment of the turbine, it becomes a challenge to design a tipshroud that will perform its intended function over the entire usefullife of the airfoil.

Two possible methods of resolving this issue are to either: 1) reducethe mechanical stresses applied to the tip shrouds by reducing theirweight, or 2) reduce the metal temperatures experienced by tip shrouds.As to the first, one common method for reducing tip shroud weight is to“scallop” (i.e., remove an indentation or a portion of) the overhangingtip shroud. The reduction in tip shroud material results in a reductionof the load applied to the connection made between the tip shroud andairfoil during operation. However, decreasing the surface area of thetip shroud through scalloping comes at a cost as it decreases theperformance of the turbine engine because a tip shroud of less surfacearea has a decreased ability to hold the turbine exhaust gas on theturbine airfoil (i.e., more of the exhaust gases slide over the top ofan airfoil that has a tip shroud of reduced surface area). In regard tothe second alternative, reducing the metal temperatures experienced bythe tip shroud by reducing the operating temperature of the gas turbinealso is an undesirable solution. As one of ordinary skill in the artwould appreciate, a reduction in operating temperature of the turbineresults in a reduction in turbine efficiency. However, reducing themetal temperatures experienced by the tip shroud by cooling it duringoperation could extend the useful life of the part.

Thus, there is a need for improved systems for cooling turbine blade tipshrouds such that the metal temperatures associated with the hightemperature turbine environment are reduced. The reduction in metaltemperatures then will allow the part to better withstand the increasedmechanical stresses associated with tip shrouds of larger surface area(i.e., unscalloped tip shrouds). Such a system would allow the tipshroud to better operate in the high temperature environment of theturbine with no scallop or the smallest scallop possible. Further, ifsuch a system could cool the tip shroud while also reducing the weightof the tip shroud, further improvements in efficiency could be realized.

BRIEF DESCRIPTION OF THE INVENTION

The present application thus describes a turbine blade that may includea tip shroud, the tip shroud having one or more cooling cavities definedtherein, an airfoil, the airfoil having at least one coolant passagedefined therein, and a plurality of exit apertures defined through anouter wall of at least one of the cooling cavities that, in use, mayallow a pressurized coolant to exit at least one of the coolingcavities. The coolant passage may extend through the airfoil such thatthe coolant passage is in fluid communication with the cooling cavity.And, the plurality of exit apertures may include at least one round exitaperture and at least one non-round exit aperture.

The present application further describes a turbine blade that mayinclude an airfoil, a tip shroud, a coolant passage that extends throughthe airfoil to the tip shroud, a continuous cooling cavity definedwithin the tip shroud and being in fluid communication with the coolantpassage, and a plurality of exit apertures defined through an outer wallof the continuous cooling cavity that, in use, allows a pressurizedcoolant to exit the continuous cooling cavity. The plurality of exitapertures may include at least one round exit aperture and at least onenon-round exit aperture. And, the continuous cooling cavity may form alabyrinth cooling circuit within the tip shroud.

These and other features of the present application will become apparentupon review of the following detailed description of the preferredembodiments when taken in conjunction with the drawings and the appendedclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and advantages of this invention will be morecompletely understood and appreciated by careful study of the followingmore detailed description of the presently preferred example embodimentsof the invention taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 is a schematic perspective view of a conventional turbine bladewith tip shroud;

FIG. 2 is a schematic plan view of conventional tip shrouds,illustrating tip shroud scalloping;

FIG. 3 is a cut-away view partly in perspective of a tip shroud having acooling cavity according to an embodiment of the invention;

FIG. 4 is a cut-away view partly in perspective of a tip shroud having acooling cavity according to an alternative embodiment of the invention;

FIG. 5 is a cut-away view partly in perspective of a tip shroud having acooling cavity according to an alternative embodiment of the invention;

FIG. 6 is a cut-away view partly in perspective of a tip shroud having acooling cavity according to an alternative embodiment of the invention;

FIG. 7 is a cut-away view partly in perspective of a tip shroud having acooling cavity according to an alternative embodiment of the invention;

FIG. 8 is a cut-away view partly in perspective of a tip shroud having acooling cavity according to an alternative embodiment of the invention;and

FIG. 9 is a cut-away view partly in perspective of a tip shroud having acooling cavity according to an alternative embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the figures, where the various numbers represent likeparts throughout the several views, FIG. 1 illustrates a typical bladewith coolant passages exiting at a blade tip to flow over a tip shroud.As schematically illustrated therein, each turbine blade 10 is comprisedof an airfoil 12 and a root 14. The airfoil 12 has a leading edge and atrailing edge. A generally concave pressure surface and a generallyconvex suction surface extend between the leading and trailing edges onopposing sides of the airfoil 12. In the illustrated example, the root14 is comprised of a shank 16 and a dovetail 18 that engages acorresponding dovetail groove on the rotor to secure the turbine blade10 to the rotor.

As shown in FIGS. 1 and 2, a tip shroud 20 is formed at the tip of theairfoil 12 and extends perpendicularly outward from the surface of theairfoil 12. The tip shroud 20 has radially inward and radially outwardfacing surfaces and is exposed to the hot compressed gas flowing throughthe turbine section. Each tip shroud 20 has bearing surfaces 22,24 overwhich it contacts the tip shroud of an adjacent blade therebyrestraining blade vibration. Furthermore, a seal rail 26 typicallyextends radially outward from the radially outward facing surface of thetip shroud 20 to prevent leakage of hot gas around the respective bladerow. In some conventional turbine blade structures, a plurality ofcooling air passages extend radially outwardly through the blade intothe blade tip. In other conventional turbine blade structures, coolantpassages may be defined in the airfoil. As shown in FIG. 2, coolantpassage may conventionally terminate in air discharge holes 28 thatallow the cooling air to discharge at the radially outward surface ofthe tip shroud 20.

FIG. 3 illustrates an exemplary embodiment of the invention. Asillustrated, the tip shroud 20 may include hollow spaces (which mayinclude chambers, cavities, apertures, and/or passageways) definedtherein. All of the hollow spaces defined within the tip shroud 20 maybe in fluid communication with each other so that the hollow spaces forma continuous cooling cavity (hereafter “cooling cavity 130”). (Note thatthe exemplary embodiments disclosed herein are generally described withreference to the function of cooling the tip shroud by passing a coolanttherethrough. This function is exemplary only and is not meant to belimiting. All of the embodiments described herein generally may beemployed for reasons other than cooling. For example, all of the hollowcavities and the structural supports configurations may be used tocreate a lightweight structurally sound tip shroud. For the sake ofbrevity, the structural elements associated with forming hollow cavitiesin a tip shroud are described herein only with reference to its“cooling” function. However, as defined herein, all such referencesshall be construed also to include the possibility of using the hollowcavity and/or any of its structural elements for advantages separatefrom the cooling function. Thus, for example, the “cooling cavity”and/or any of its described structural elements may be used for thefunction of creating a lightweight structurally sound hollow tip shroudand not for the purposes of cooling the tip shroud. This is true whetherthe reference to a cooling function is made in the detailed descriptionor the claims or any other part of this application.) In someembodiments, the cooling cavity 130 may include a pressure side coolingcavity 132 and a suction side cooling cavity 134 that coinciderespectively with the pressure side and suction side of the airfoil 12.As illustrated, the pressure side cooling cavity 132 and the suctionside cooling cavity 134 may be in fluid communication with each otheralong a trailing or aft edge 136 of the airfoil 112.

In a conventional manner, air may be taken into the turbine blade 10near the dovetail 18 or shank 16 area and flow through the airfoil 12toward the tip shroud 20. In the illustrated example, a coolant chamber138 may be defined at the approximate center of the tip shroud 20(substantially separating the pressure side cooling cavity 132 and thesuction side cooling cavity 134) as a coolant (generally compressed air)reservoir for distribution through the tip shroud 20 via the pressureside cooling cavity 132 and the suction side cooling cavity 134. As analternative, the coolant chamber 138 may be defined in the tip of theairfoil 12 (this embodiment is not shown). As a further alternative, theplurality of coolant passages extending through the airfoil 12 may bedirectly coupled to the pressure side cooling cavity 132 and the suctionside cooling cavity 134 such that no coolant chamber 138 is present (seediscussion below associated with the embodiment of FIG. 4).

The coolant then may flow from the coolant chamber 138 or the respectivecoolant passages to and through the cooling cavities 132,134. In theillustrated example, a plurality of coolant chamber apertures 140 aredefined between the coolant chamber 138 and the cooling cavities132,134. Thus, the coolant chamber 138, the pressure side cooling cavity132, and the suction side cooling cavity 134 are all in fluidcommunication with each other. As such, as defined and used herein, thecoolant chamber 138, the pressure side cooling cavity 132, and thesuction side cooling cavity 134 form a single cooling cavity or acontinuous cooling cavity in the tip shroud 20 (i.e., because all of thedefined cavities/chambers/apertures/passageways within the tip shroud 20are in fluid communication with each other). The coolant chamberapertures 140 connecting the cooling cavities 132,134 to the coolantchamber 138 may be used not only to simply connect the cooling cavities132,134 to the coolant chamber 138, but may also be adapted to meter orcontrol the flow into the cooling cavities 132,134 such that a desirabledistribution of coolant throughout the tip shroud 20 is realized. In thealternative, the coolant chamber 138 may be open to the cooling cavities132,134, as discussed later.

The cooling cavity 130 may have a plurality of support ribs or ribs142,144 defined therein. In general, the ribs 142,144 are elongatedstructures that connect the floor (or radial floor) of the coolingcavity 130 to the ceiling (or radial ceiling) of the cooling cavity 130,as illustrated in the several figures. (As used herein, the floor of thecooling cavity 130 is illustrated in the several figures as the areaaround the ribs. The ceiling of the cooling cavity 130 is the portionthat has been removed from the tip shroud 20 so that a view of theinterior of the cooling cavity 130 may be provided.) One of thefunctions of the ribs 142,144 is to advantageously define the shape ofthe cooling cavity 130. Also, the ribs 142,144 maintain the structuralstrength of the hollow tip shroud 20 so that the useful life of theturbine blade 10 is not negatively impacted. The ribs 142,144 supportthe hollow areas of the cooling cavity 130, which allows the tip shroud20 to be lightweight. Lightweight tip shrouds are advantageous as theyreduce mechanical stresses in both the tip shroud 20 and the airfoil 12during operation. Generally, as described in more detail below, the ribs142,144 extend partially across the cooling cavity 130 in which they arelocated. In some embodiments, a plurality of the ribs 142,144 may extendacross a majority of the distance across the cooling cavity 130. In someembodiments, the ribs 142,144 are approximately parallel to each other.

As illustrated, the ribs 142,144 may include a plurality of truncatedribs 142. Truncated ribs 142 generally are shorter ribs, which in someembodiments (and as illustrated), define exit apertures 147. Inaddition, the ribs 142,144 may include a plurality of partition ribs 144that are substantially longer than the truncated ribs 142. (Note thatsome embodiments may include only a plurality of partition ribs 144. Insuch embodiments, holes bored at the edge of the tip shroud 20 maydefine the exit apertures 147.) In general and as illustrated, thepartition ribs 144 are of a length such that they extend across at leasta majority of the distance across the respective cooling cavity 132,134,but do not extend across the entire distance. In some embodiments, thepartition ribs 144 may extend across at least 75% of the width acrossthe cooling cavity 130. Thus, partition ribs 144 do not create separatecavities. In other words, the hollow space on either side of a partitionrib 144 remains in fluid communication around at least one end of thepartition rib 144.

As illustrated in FIG. 3, the partition ribs 144 may include an outwardextending partition rib 145. The outward extending partition rib 145generally may extend outwardly from the wall defining the coolantchamber 138 to a position short of the outer wall of the cooling cavity130, thus defining a space or gap between the outward extendingpartition rib 145 and the outer wall of the cooling cavity 130. In someembodiments, the outer wall of the cooling cavity 130 may be defined byone of the truncated ribs 142. In such embodiments, the outwardextending partition rib 145 may extend from the wall defining thecoolant chamber 138 to a position short of the truncated rib 142 thatdefines the outer wall of the cooling cavity 130 at that location, thusdefining gap between the outward extending partition rib 145 and thetruncated rib 142. The partition ribs 144 also may include an inwardextending partition rib 146, which generally extends inwardly from theouter wall of the cooling cavity 130 to a position short of the walldefining the coolant chamber 138, thus defining a gap between the inwardextending partition rib 146 and the wall defining the coolant chamber138. In some embodiments, both of the gaps defined by: 1) the outwardextending partition rib 145 and the outer wall of the cooling cavity 130and 2) the inward extending partition rib 146 and the wall defining thecoolant chamber 138 may measure approximately 0.10 to 0.25 inches. Inother embodiments, both the gaps defined by: 1) the outward extendingpartition rib 145 and the outer wall of the cooling cavity 130 and 2)the inward extending partition rib 146 and the wall defining the coolantchamber 138 may measure at least 0.10 inches.

As illustrated, each of the cooling cavities 132,134 may contain aplurality of partition ribs 144. In some embodiments (and asillustrated), each of the cooling cavities 132,134 may contain between4-7 partition ribs 144. Further, as illustrated, the partition ribs 144may be configured in an alternating arrangement. In an alternatingarrangement, the placement of outward extending partition ribs 145generally alternates with the placement of inward extending partitionribs 146. As used herein, an “alternating arrangement” shall beconstrued broadly to including several different alternatingconfigurations and is not meant to be limited to strict “one for one”alternating (i.e., the arrangement requiring that each outward extendingpartition rib 145 be neighbored by only inwardly extending partitionribs 146). As used herein, an “alternating arrangement” shall also beconstrued to describe, for example, the following sequence of partitionribs: an outward extending partition rib 145—an outward extendingpartition rib 145—an inward extending partition rib 146—an outwardextending partition rib 145—an outward extending partition rib 145—aninward extending partition rib 146. In another case, for example, an“alternating arrangement” may be used to describe this sequence: aninward extending partition rib 146—an outward extending partition rib145—an outward extending partition rib 145—an inward extending partitionrib 146—an inward extending partition rib 146—an outward extendingpartition rib 145—an outward extending partition rib 145. “Alternatingarrangement” may be used to describe other similar sequences. Thealternating arrangement strategy may effectively define a tortuous orlabyrinth cooling circuit through the cooling cavities 132,134, whichmay be advantageous in the cooling of the tip shroud 20 via thecirculation of a coolant therethrough. As used herein, a labyrinthcircuit is defined generally to describe a winding or circuitous paththat impedes flow, which, as described in more detail below, may be usedadvantageously to effectively distribute coolant throughout the tipshroud 20 during operation.

As noted above, between adjacent truncated ribs 142, exit apertures 147may be defined for coolant flow out of the turbine blade 10. The coolingcavities 132,134, as illustrated, are disposed primarily in the plane ofthe tip shroud 20.

FIG. 4 illustrates an alternative embodiment of the present applicationthat does not include the coolant chamber 138 of the embodimentdiscussed above. The embodiment of FIG. 4 generally may include theplurality of truncated ribs 142 and partition ribs 144 in similararrangement to that discussed above in relation of FIG. 3. However,instead of the wall defining the coolant chamber 138, the embodiment ofFIG. 4 may have an interior center wall 152. The interior center wall152 generally bisects the cooling cavity 130, thus creating (as thecoolant chamber 138 did in the embodiment of FIG. 3) the pressure sidecooling cavity 132 and the suction side cooling cavity 134 on each sideof it. With no coolant chamber 138, the coolant passages extendingthrough the airfoil 12 may be directly coupled to the pressure sidecooling cavity 132 and the suction side cooling cavity 134 through aplurality of entry apertures 154. As illustrated, the entry apertures154 may be located along the wall of the interior center wall 152. Otherlocations are possible, such as the floor of the cooling cavities 132,134.

Further, in the embodiment of FIG. 4, the outward extending partitionrib 145 generally extends outwardly from the interior center wall 152 toa position short of the outer wall of the cooling cavity 130. In someembodiments and as illustrated, the outer wall of the cooling cavity 130may be defined by one of the truncated ribs 142. In such embodiments,the outward extending partition rib 145 of FIG. 4 may extend from theinterior center wall 152 to a position short of the truncated rib 142that defines the outer wall of the cooling cavity 130 at that location,thus defining a gap between the outward extending partition rib 145 andthe truncated rib 142. Also, in the embodiment of FIG. 4, the inwardextending partition rib 146 generally extends inwardly from the outerwall of the cooling cavity 130 to a position short of the interiorcenter wall 152, thus defining a gap between the inward extendingpartition rib 146 and the interior center wall 152. Finally, similar tothe embodiment of the FIG. 3, the partition ribs 144 may be arrangedsuch the placement of an outward extending partition rib 145 alternateswith the placement of an inward extending partition rib 146.

Alternative embodiments are illustrated in FIGS. 5 through 9. Theseembodiments illustrate the application of some of the features discussedabove within cooling cavities 130 of a different configuration as wellas the use of new elements as described in detail below. Both theembodiments illustrated in FIGS. 3 and 4 have a dividing feature in theapproximate center of the tip shroud 20 (i.e., in FIG. 3 the dividingfeature is the coolant chamber 138 and in FIG. 4 the dividing feature isthe interior center wall 152). In some embodiments, like those of FIGS.5 through 8, a dividing feature may not be present.

FIG. 5 illustrates an alternative embodiment of a single or continuouscooling cavity 130 in a tip shroud 20 with a plurality of partition ribs144. A plurality of truncated ribs 142 also may be present. Thetruncated ribs 142 may define exit apertures 147 that are concentratedalong the pressure side and suction side of the tip shroud 20. With nocoolant chamber 138, the coolant passages that extend through theairfoil 12 may be directly coupled to the cooling cavity 130 through aplurality of entry apertures 154. As illustrated, the entry apertures154 may be located toward the center of the tip shroud 20, on eitherside of an approximate centerline of the tip shroud 20 that if drawnwould roughly separate the suction side of the tip shroud 20 with thepressure side of the tip shroud 20, though other locations are possible.

Further, in the embodiment of FIG. 5, the partition ribs 144 areconfigured such that they originate along the outer wall of the coolingcavity 130 (i.e., a first interior wall) and extend across the tipshroud 20 toward the opposing outer wall of the cooling cavity 130(i.e., a second interior wall). The partition ribs 144 may be of alength such that they terminate in a position short of the opposingouter wall of the cooling cavity 130. Thus, a narrow space or gap may bedefined at the end of the partition rib 144 between the partition rib144 and the opposing outer wall of the cooling cavity 130. In someembodiments and as illustrated, the outer wall of the cooling cavity 130may be defined by one of the truncated ribs 142. In such embodiments,the partition rib 144 may extend toward the truncated rib 142 of theopposing outer wall of the cooling cavity 130 to a position short of thetruncated rib 142 that defines the outer wall of the cooling cavity 130at that location, as illustrated in FIG. 5. Thus, a narrow space or gapmay be defined at the end of the partition rib 144 between the partitionrib 144 and the opposing truncated rib 142. Further, as illustrated inFIG. 5, the partition ribs 144 may be configured in an alternatingarrangement. In this arrangement, the placement of a partition rib 144that extends from one of the outer walls of the cooling cavity 130alternates with the placement of a partition rib 14 that originates fromthe opposing outer wall of the cooling cavity 130. See also thedefinition for “alternating arrangement” provided above. As before, thisalternating arrangement strategy through the cooling cavity 130 mayeffectively define a tortuous or labyrinth cooling circuit, which may beadvantageous in the cooling of the tip shroud 20 via the circulation ofa coolant therethrough. Note that in alternative embodiments, thealternating partition ribs 144 may be oriented so that they generallywould align perpendicularly to the orientation of the partition ribs 144as illustrated in FIG. 5. As one of ordinary skill in the art willappreciate, other arrangements are also possible.

FIGS. 6-8 illustrate several exemplary embodiments that include discretestructural elements within a tip shroud cooling cavity 130. As usedherein, a discrete structural element is an element that structurallyconnects the floor of the cooling cavity 130 to the ceiling of thecooling cavity 130 and that does not originate from, terminate in, orconnect to an interior wall of the cooling cavity 130 or the outer edgeor periphery of the tip shroud 20. For the purpose of this definition,an interior wall of the cooling cavity 130 may include: 1) the walldefining the coolant chamber 138; 2) the outer wall of the coolingcavity 130; 3) the interior center wall 152; or 4) other similar wallsthat may be defined within the cooling cavity 130. Also, as used hereinand previously stated, the ceiling of the cooling cavity 130 is theelement that has been removed in FIGS. 3-9 so that the interior of thecooling cavity 130 may be observed. In other words, discrete structuralelements generally are structural elements that, except for theconnections the structural element makes with the floor and ceiling ofthe cooling cavity 130, are surrounded by the hollow area of the coolingcavity 130.

FIG. 6 illustrates a single or continuous cooling cavity 130 with aplurality of discrete partition ribs 202. The discrete partition ribs202 are discrete structural elements because they connect the floor ofthe cooling cavity 130 to the ceiling of the cooling cavity 130 and donot originate from, terminate in, or connect to an interior wall of thecooling cavity 130 or the outer edge of the tip shroud 20. In someembodiments and as shown, a plurality of truncated ribs 142 also may bepresent. The truncated ribs 142 may define exit apertures 147 that areconcentrated along the pressure side and suction side of the tip shroud20. With no coolant chamber 138 in the embodiment of FIG. 6, the coolantpassages that extend through the airfoil 12 may be directly coupled tothe cooling cavity 130 through a plurality of entry apertures 154. Asillustrated, the entry apertures 154 may be located along an approximatecenterline of the tip shroud 20 that, if drawn, would approximatelyseparate the suction side of the tip shroud 20 with the pressure side ofthe tip shroud 20.

Further, in the embodiment of FIG. 6, the discrete partition ribs 202may be configured such that each begins at the approximate center of thecooling cavity 130 and extends outward toward opposing outer walls ofthe cooling cavity 130. The discrete partition ribs 202 may extendacross at least a majority of the distance across the cooling cavity130. In some embodiments, the discrete partition ribs 202 may extendacross at least 75% of the width of the cooling cavity 130. In otherembodiments, the discrete partition ribs 202 may be oriented so thatthey generally would align perpendicularly to the discrete partitionribs 202 illustrated in FIG. 6. As one of ordinary skill in the art willappreciate, other arrangements are also possible. The discrete partitionribs 202 may be of a length such that at one end they terminate in aposition short of the outer wall of the cooling cavity 130 and at theother end they terminate in a position short of the opposing outer wallof the cooling cavity 130. Thus, two gaps may be defined at the end ofeach of the discrete partition ribs 202 (i.e., a first gap defined bythe end of the discrete partition rib 202 and the outer wall of thecooling cavity 130; and a second gap defined by the other end of thediscrete partition rib 202 and the opposing outer wall of the coolingcavity 130). In some embodiments, the first and second gap each maymeasure approximately 0.10 to 0.75 inches. In other embodiments, thefirst and second gap each may measure at least 0.10 inches. In someembodiments and as illustrated, the outer wall of the cooling cavity 130may be defined by one of the truncated ribs 142. In such embodiments,the discrete partition rib 202 may extend toward opposing outer walls ofthe cooling cavity 130 to a position just short of the truncated rib 142that defines the outer wall of the cooling cavity 130 at that location,as illustrated in FIG. 6.

FIG. 7 illustrates a single or continuous cooling cavity 130 with aplurality of discrete truncated ribs 206. The discrete truncated ribs206 are, as defined above, discrete structural elements because theyconnect the floor of the cooling cavity 130 to the ceiling of thecooling cavity 130 and do not originate from, terminate in, or connectto an interior wall of the cooling cavity 130 or the outer edge of thetip shroud 20. In some embodiments (though not shown in FIG. 7), aplurality of truncated ribs that define exit apertures 147 also may bepresent. The truncated ribs 142 that define exit apertures 147 (as shownin previous embodiments) are not considered discrete structuralelements, as defined herein, because they generally terminate in theouter edge or the periphery of the tip shroud 20. With no coolantchamber 138 in the embodiment shown in FIG. 7, the coolant passages thatextend through the airfoil 12 may be directly coupled to the coolingcavity 130 through a plurality of entry apertures 154. As illustrated,the entry apertures 154 may be located along an approximate centerlineof the tip shroud 20 that, if drawn, would approximately separate thesuction side of the tip shroud 20 with the pressure side of the tipshroud 20.

As illustrated in FIG. 7, a plurality of the discrete truncated ribs 206may be spaced throughout the cooling cavity 130 so that a minimum gap ismaintained between each. The gaps that are maintained between each ofthe discrete truncated ribs 206 may be at least 0.05 inches. Thediscrete truncated ribs 206 may be rectangular in nature (with roundedcorners in some embodiments), as shown in FIG. 7. In some embodiments,the discrete truncated ribs 206 may be approximately 0.10 to 0.75 incheslong and 0.05 to 0.25 inches wide. In some embodiments and asillustrated in FIG. 7, between 15 and 25 discrete truncated ribs 206 maybe defined within the cooling cavity 130.

FIG. 8 illustrates a single or continuous cooling cavity 130 with aplurality of discrete columns 208. The discrete columns 208 are, asdefined above, discrete structural elements because they connect thefloor of the cooling cavity 130 to the ceiling of the cooling cavity 130and do not originate from, terminate in, or connect to an interior wallof the cooling cavity 130 or the outer edge of the tip shroud 20. Withno coolant chamber 138 in the embodiment shown in FIG. 8, the coolantpassages that extend through the airfoil 12 may be directly coupled tothe cooling cavity 130 through a plurality of entry apertures 154. Asillustrated, the entry apertures 154 may be located along an approximatecenterline of the tip shroud 20 that, if drawn, would approximatelyseparate the suction side of the tip shroud 20 with the pressure side ofthe tip shroud 20.

As illustrated in FIG. 8, a plurality of the discrete columns 208 may bespaced throughout the cooling cavity 130 so that a minimum gap ismaintained between each of the discrete columns. The minimum gap that ismaintained between each of the discrete columns 208 may be at least 0.05inches. As illustrated, the discrete columns 208 may have a circularcross-section. In such embodiments, the diameter of the circularcross-section may measure approximately 0.05 to 0.25 inches. In otherembodiments, the discrete columns 208 may have a square-shapecross-section. In such embodiments, each of the sides of thesquare-shaped cross-section may measure approximately 0.05 to 0.25inches. In some embodiments and as illustrated in FIG. 8, between 5 and50 discrete columns 206 may be defined within the cooling cavity 130.

FIG. 9 illustrates an exemplary embodiment that demonstrates the use ofround exit apertures 212 and non-round exit apertures 214 with a tipshroud cooling cavity 130. As previously described, between adjacenttruncated ribs 142 or through the outer wall of the cooling cavity 130,a plurality of exit apertures 212,214 may be defined for the pressurizedcoolant to exit the cooling cavity 130. As shown in the exampleembodiment of FIG. 9, non-round exit apertures 214 may be defined. Thesenon-round exit apertures 214 may be rectangular in shape (someembodiments may have rounded corners), as illustrated. Not shown, thenon-round exit apertures 214 also may be elliptical or oval in shape.The non-round exit apertures 214 may provide heat transfer benefits overround exit apertures. As illustrated in FIG. 9, one or more of the roundexit apertures 212 also may be defined. Additional round exit apertures212 and non-round exit apertures 214 may be provided. As one of ordinaryskill in the art will appreciate, different arrangements of the roundexit apertures 212 and non-round exit apertures 214 also may bepossible.

Note that the embodiments described in FIGS. 3 through 9 all provideexamples of a tip shroud with a single or continuous cooling cavity.Certain of the features discussed therein, however, are not limited inuse to a single or continuous cooling cavity (i.e., may be usedsuccessfully in tip shrouds that have multiple separated coolingcavities that are not in fluid communication with each other). Thesefeatures include: 1) ribs that extend partially across a cooling cavitysuch that they create a passageway between the end of the rib and anopposing structure; 2) the alternating arrangement of the ribs thatextend partially across a cooling cavity; 3) the discrete structuralelements; and 4) the use of non-round exit apertures and round exitapertures. The description of these features in relation to a single orcontinuous cooling cavity is exemplary only and not meant to belimiting.

In use, coolant (generally compressed air) may be distributed to theturbine blade 10. The coolant may travel through the coolant passages tothe coolant chamber 138. The coolant may then be delivered to thecooling cavity 130 through the coolant chamber apertures 140. (Note thatin the embodiments described by FIG. 4 through 8, the coolant isdelivered directly to the cooling cavity 130 through the entry apertures154.) Once in the cooling cavity 130, the coolant flows around the ribs142,144 as necessary toward the exit apertures 147 and then exits thetip shroud 20 via the exit apertures 147, which generally are positionedalong the outer wall of the cooling cavity 130. This flow of coolantthrough the cooling cavity 130 convectively cools the tip shroud 20.

As one of ordinary skill in the art will appreciate, the pressureconditions that exist at the edges of the tip shroud 20 vary greatlyduring operation of the turbine. The external pressure is high at theleading edge (shown in both FIGS. 3 and 4 as 170) of the tip shroud 20,low at the trailing edge (shown in both FIGS. 3 and 4 as 180) of the tipshroud 20, and moderate at the edges of the tip shroud 20 between theleading and trailing edges (shown in both FIGS. 3 and 4 as 190). Thecooling cavity 130 of the tip shroud 20 has a higher pressure than theexternal pressure, however without intervention, much of the coolantwill exit near the trailing edge 180 of the tip shroud 20 where theexternal pressure is the lowest. This tendency can cause an insufficientamount of coolant to exit the leading edge 170 of the tip shroud 20,which may result in excessive temperatures in those areas that maynegatively impact the useful life of the turbine blade 10. Thus, it isdesirable to cause the coolant to be preferentially distributedthroughout the tip shroud 20 as it exits the turbine blade 10.

The arrangement of the ribs 142,144, as described in the embodimentsabove, generally creates a torturous or labyrinth cooling circuit thatthe coolant entering the tip shroud 20 must navigate before exiting. Forexample, coolant entering the tip shroud 20 near the leading edge 170must navigate through the labyrinth cooling circuit to exit at the lowerpressure trailing edge 180. In this way, the torturous path or labyrinthcooling circuit creates an impediment that discourages adisproportionate amount of the coolant from exiting at the low pressureof the trailing edge 180. The result is that coolant exits the tipshroud 20 along all of the different pressure regions of the tip shroud20, which creates a preferential distribution of coolant throughout thetip shroud 20 during operation. This beneficial result is achievedwithout necessitating multiple independent or disconnected coolingcavities (i.e., cooling cavities not in fluid communication with eachother) within the tip shroud 20. As one of ordinary skill in the artwill appreciate, turbine blades with hollow cooling cavities generallyare manufactured by an investment casting process. Having a single orcontinuous cooling cavity instead of multiple disconnected cavitiesallows for certain advantages to be realized in the investment castingprocess.

A further benefit of the alternating arrangement of the partition ribs144 is that the free ends 194 of each of the partition ribs 144 areshielded by the partition rib 144 to each side of it, increasing thestructural integrity of the tip shroud 20. The free end 194 of thepartition rib 144 refers to the end that terminates at an open areawithin the cooling cavity 130 (see the free end 194 labeled in FIGS. 3,4 and 5). In other words, the free end 194 is the end of the partitionrib 144 that is opposite to the end that originates from a an interioror exterior wall in the continuous cooling cavity 130 (“interior orexterior wall of the continuous cooling cavity 130 may includes, forexample, either: 1) the outer wall of the cooling cavity 130; 2) thewall of the coolant chamber 138; or 3) the interior center wall 152). Asone of ordinary skill in the art will appreciate, terminating thepartition rib 144 in an open area within the continuous cooling cavity130 creates an area of increased stress. The loading that results inthis stress, however, may be handled by the neighboring partition rib144, which, because of the alternating arrangement of the partition ribs144, may not terminate in the same area within the cooling cavity. Thisserves to reduce the local concentrations of stress that would haveotherwise been realized at the termination of one of the partition ribs144.

While the invention has been described in connection with what ispresently considered to be the most practical and preferred embodiment,it is to be understood that the invention is not to be limited to thedisclosed embodiment, but on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims. For example, while reference has been madein particular to the cooling of a tip shroud, the technology disclosedherein could be used on a tip shroud that is not located at the tip ofthe blade. In this regard, some blades have tip shrouds about mid-lengthof the airfoil that connect it to its adjacent blade, and the coolantpassages described hereinabove could be incorporated therein.

1. A turbine blade, comprising: a tip shroud, the tip shroud having oneor more cooling cavities defined therein; an airfoil, the airfoil havingat least one coolant passage defined therein; and a plurality of exitapertures defined through an outer wall of at least one of the coolingcavities that, in use, allows a pressurized coolant to exit at least oneof the cooling cavities; wherein: the coolant passage extends throughthe airfoil such that the coolant passage is in fluid communication withthe cooling cavity; the plurality of exit apertures includes at leastone round exit aperture and at least one non-round exit aperture; all ofthe cooling cavities defined within the tip shroud are in fluidcommunication with each other and define a cooling cavity; the coolingcavity comprises a plurality of ribs formed therein, the ribs beingsized and configured such that at least some of the ribs extend apartial way across the distance across the cooling cavity; the coolingcavity comprises a pressure side cooling cavity, a suction side coolingcavity, and a coolant chamber, the coolant chamber comprising a chamberthat resides substantially between the pressure side cooling cavity andthe suction side cooling cavity; the coolant chamber is in fluidcommunication with the coolant passage; and the coolant chamber is influid communication with the pressure side cooling cavity and a suctionside cooling cavity via a plurality of coolant chamber apertures.
 2. Theturbine blade according to claim 1, wherein the non-round exit aperturecomprises a general rectangular shape.
 3. The turbine blade according toclaim 2, wherein the rectangular shape comprises a size that isapproximately 0.05 to 0.30 inches long and 0.03 to 0.10 inches wide. 4.The turbine blade according to claim 1, wherein the non-round exitaperture comprises a general elliptical shape.
 5. The turbine bladeaccording to claim 1, wherein: the cooling cavity comprises a pluralityof ribs formed therein; the ribs comprise elongated structures thatconnect the floor of the cooling cavity to the ceiling of the coolingcavity; and the ribs are configured such that a labyrinth coolingcircuit is formed within the cooling cavity.
 6. The turbine bladeaccording to claim 1, wherein the ribs are sized and configured suchthat at least some of the ribs extend a partial way across the distanceacross the cooling cavity and across at least a majority of the distanceacross the cooling cavity.
 7. The turbine blade according to claim 1,wherein: the ribs comprise a plurality of partition ribs; and thepartition ribs are sized and configured such that at least a pluralityof the partition ribs extends across at least a majority of the distanceacross the cooling cavity.
 8. The turbine blade according to claim 7,wherein: the partition ribs comprise a plurality of outward extendingpartition ribs and a plurality of inward extending partition ribs; atleast some of the outward extending partition ribs originate from a walldefining the coolant chamber and extend outwardly to a position short ofan outer wall of the cooling cavity, thus defining a first gap betweenthe outward extending partition rib and the outer wall of the coolingcavity; and at least some of the inward extending partition ribsoriginate from the outer wall of the cooling cavity and extend inwardlyto a position short of the wall defining the coolant chamber, thusdefining a second gap between the inward extending partition rib and thewall defining the coolant chamber.
 9. The turbine blade according toclaim 8, wherein: the outer wall of the cooling cavity is partiallydefined by one or more truncated ribs, the truncated ribs beingsubstantially shorter than the partition ribs; and at least some of theoutward extending partition ribs originate from the wall defining thecoolant chamber and extend to a position short of the truncated rib thatdefines the outer wall of the cooling cavity, thus defining a gapbetween the outward extending partition rib and the truncated rib. 10.The turbine blade according to claim 1, further comprising an interiorcenter wall, the interior center wall partially separating the coolingcavity such that a pressure side cooling cavity is formed on one side ofthe interior center wall and a suction side cooling cavity is formed onthe other side of the interior center wall; wherein the ribs comprise aplurality of partition ribs.
 11. The turbine blade according to claim10, wherein: the partition ribs comprise a plurality of outwardextending partition ribs and a plurality of inward extending partitionribs; each of the outward extending partition ribs originates from theinterior center wall and extends outwardly to a position short of anouter wall of the cooling cavity, thus defining a first gap between theoutward extending partition ribs and the outer wall of the coolingcavity; and each of the inward extending partition ribs originates fromthe outer wall of the cooling cavity and extends inwardly to a positionshort of the interior center wall, thus defining a gap between theinward extending partition ribs and the interior center wall.
 12. Theturbine blade according to claim 1, wherein: the cooling cavitycomprises a plurality of ribs, the ribs comprising elongated structuresthat connect the floor of the cooling cavity to the ceiling of thecooling cavity; and the cooling cavity comprises a first interior wallthat generally opposes a second interior wall across the cooling cavity;the ribs are configured such that some of the ribs originate at thefirst interior wall of the cooling cavity and extend toward the secondinterior wall of the cooling cavity and some of the ribs originate atthe second interior wall of the cooling cavity and extend toward thefirst interior wall of the cooling cavity; and the ribs are sized andconfigured such that some of the ribs extend across at least a majorityof the distance across the cooling cavity.
 13. The turbine bladeaccording to claim 12, wherein the ribs are arranged such that theplacement of a rib that originates on the first interior wall of thecooling cavity generally alternates with the placement of a rib thatoriginates on the second interior wall of the cooling cavity.